Mark III - Volume Pot Mod - R2, yeap, yet again...

[jjschessmaster]

Hey all, did the r2 mod amd wired it up as directed. I tend to have max the r2 volume and still seeing a drop in volume when r1 volume is around 8+. Anyone else seeing this? Its certainly better and i can drop r2 no problem, but its not a huge jump up in r2 volume unless i drop the front volume. Any thoughts? Using mullard tubes for all, master is pretty low (1.5-2), fairly high output pickups if that influences this?

 

[Donnie B.]

I did this mod on my Short Head Mark III with very positive results.

I also did this on a Red III Short Head. I wanted to keep both the reverb and presence active so I put
the 250K audio pot where the DI out Volume was.

Really don't understand anyone (yet alone Mike B.) saying it couldn't be done.

 

[Foolk]

Hi everyone,

I just bought a Mark 3 combo which has some mods on it. One of them is R2 volume pot.

I don't know if i'm going to keep it this way... May i'm going to undo this mod.

I have a 60W combo, blue stripe, without equalizer. My question is : do you know what is the original value of the R130 resistor for my model ?

Here is a picture of the mod (purple + black wire going to the pot)


The pot :


Thanks

 

[Foolk]

I forgot to say that "my" mod is different than the mod described in the original post : nothing is wired to the R131.

 

[Rob S]

(Shortened)…And here's my series of photos and notes; as mentioned before, you essentially replace the R130 with a pot using one spot from the old R130 'lugs' and I used a spot from R131 just because I had more room to solder there and that was it. I left the old R130 there (just snipped and out of the way) and no I wouldn't go on a 'world tour' with my amp as is but it works and makes the ability to balance the 3 Channels perfect,

Hi, and thanks for the nice description!

I’m new to the forum as a member (have been reading for quite a while before) and want to perform the R2 Volume mod on my Mark III red stripe DRGX 15“ head.

I already did some work on it but it’s technically still in stock condition as far as I know.

The Volume mod is mainly on my list because I want to balance out R1 and Lead (R1 is quite loud when you dial in a heavy Lead tone).
In theory the mod should only affect R2 but from what I found so far, it seems to be active on R1 too!?

If I understood it right, I could place the pot on the two connections of R130 OR place it as shown in the picture above with the other terminal on R131 right?

Thanks for your help guys!

 

[Rob S]

Okay, I did the mod today anyway and went for the placement at both lugs of R130…

What it does now is exactly what it says:

You can adjust the Volume of R2 when it is activated. No affects on anything else :-/

I sourced a genuine Mark IV Treble pot with the matching knob for the mod btw.

Having no effect in R1 is a bit of a bummer tho.

Should I try again and move the center wire of the pot to the right side of R131 (looking from the back of the chassis at it)? I’m not sure but I really wished it had an impact on R1, too.

I mean if I take a look at the schematic I have at hand it should be a different story- that’s why I was asking you guys if there is a difference between the two ways to connect the R2 volume pot as mentioned in the opening post.

Would be nice if someone could explain this from his experience.

Best regards